The present invention relates to Satellite positioning apparatus for mobile units and a navigation system equipped with a feature to calculate the reckoned position of a mobile unit after it has traveled.
In recent years, a computing system is mounted on a mobile unit which makes executable a variety of application software such as audio apparatus, television sets or navigation systems, according to the user's needs.
When the computing system executes application software of navigation, satellite positioning apparatus for mobile units is used to measure the absolute position of the mobile unit, traveling speed, and heading, etc.
FIG. 4 shows an example of use of conventional satellite positioning apparatus for mobile units. The satellite positioning apparatus for mobile units (positioning section) 51 calculates the "position, traveling speed, and heading" of the mobile unit by tracking signals received from GPS satellites via a GPS antenna 52. The satellite positioning apparatus for mobile units 51 then outputs the calculation results as GPS data output to the support module 55 of a car computing system 54 via a serial line 53. In case three satellites are acquired, two-dimensional positioning is allowed. In case four or more satellites are acquired, three-dimensional positioning is allowed. Positioning data calculated via two-dimensional positioning includes "latitude and longitude." Positioning data calculated via three-dimensional positioning includes "latitude, longitude, and altitude.
The CPU module 56 of the car computing system executes application software of car navigation to provide voice guidance and map display to the user.
The data I/O of the satellite positioning apparatus for mobile units 51 generally uses a universal asynchronous receiver/transceiver (UART). An interface is provided by a protocol control information (PCI) bus between the support module 55 which receives serial data output from the UART and the CPU module 56.
This example, however, has a problem that the car computing system 54 can use only data from the satellite positioning apparatus for mobile units 51 in order to execute application software of car navigation, resulting in reduced car position reckoning capability compared with a system dedicated for car navigation.
This is because, in a system dedicated for car navigation, the dead reckoning (DR) procedure is followed. The DR collects information from a gyro sensor and a speed sensor on a car to reckon the travel distance and heading of the car in addition to the absolute position information input to the satellite positioning apparatus for mobile units 51 for deciding the position of the car then makes map matching on the overall results obtained from such information.